Drilling and producing offshore oil and gas wells includes the use of offshore facilities for the exploitation of undersea petroleum and natural gas deposits. Offshore systems often include a marine riser which connects surface equipment to a blowout preventer stack which is connected to a subsea wellhead.
Offshore systems are frequently equipped for well testing operations and include a safety shut-in system which automatically prevents fluid communication between the subsea wellhead and the surface. A typical safety shut-in system comprises a subsea test tree which is lowered through the riser and landed inside the blowout preventer stack.
A subsea test tree typically includes one or more safety valves that can automatically shut-in a well in the event of an emergency, such as a natural disaster. Hydraulic, electrical and fiber optic communications to, inter alia, operate the valves and devices in a blowout preventer stack are communicated from a surface control system by way of an umbilical.
Normally, when a subsea test tree is utilized in subsea applications, the subsea test tree comprises a subsea controller (e.g., multiplex controller) and umbilical system lowered with the subsea test tree and contained wholly within the marine riser. The subsea controller and umbilical system serve to operate the subsea test tree. These in-marine riser systems must work for extended periods of time with multiple installation and removal cycles within the confined space of a blowout preventer.
In addition, due to containment within the marine riser, the subsea controller and umbilical system must be designed to withstand both the fluids and temperatures associated with the harsh in-riser environment. Due to the unforgiving conditions, the typical life span for the subsea controller and umbilical system is less than two years.
Accordingly, there exists a need for a subsea controller and umbilical system that does not subject the devices to the harsh in-marine riser conditions and still provides for appropriate hydraulic, electrical and fiber optic communications to the valves and devices within a blowout preventer stack, including a subsea test tree.